US7839907B2 - Laser driving apparatus - Google Patents

Laser driving apparatus Download PDF

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US7839907B2
US7839907B2 US12/465,244 US46524409A US7839907B2 US 7839907 B2 US7839907 B2 US 7839907B2 US 46524409 A US46524409 A US 46524409A US 7839907 B2 US7839907 B2 US 7839907B2
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value
temperature setting
efficiency
setting value
temperature
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US20090290609A1 (en
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Shuji Inoue
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Godo Kaisha IP Bridge 1
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Panasonic Corp
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/04—Processes or apparatus for excitation, e.g. pumping, e.g. by electron beams
    • H01S5/042—Electrical excitation ; Circuits therefor
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/35—Non-linear optics
    • G02F1/3501—Constructional details or arrangements of non-linear optical devices, e.g. shape of non-linear crystals
    • G02F1/3505—Coatings; Housings; Supports
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/005—Optical components external to the laser cavity, specially adapted therefor, e.g. for homogenisation or merging of the beams or for manipulating laser pulses, e.g. pulse shaping
    • H01S5/0092—Optical components external to the laser cavity, specially adapted therefor, e.g. for homogenisation or merging of the beams or for manipulating laser pulses, e.g. pulse shaping for nonlinear frequency conversion, e.g. second harmonic generation [SHG] or sum- or difference-frequency generation outside the laser cavity
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/04—Processes or apparatus for excitation, e.g. pumping, e.g. by electron beams
    • H01S5/042—Electrical excitation ; Circuits therefor
    • H01S5/0428—Electrical excitation ; Circuits therefor for applying pulses to the laser
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/06—Arrangements for controlling the laser output parameters, e.g. by operating on the active medium
    • H01S5/068—Stabilisation of laser output parameters
    • H01S5/0683—Stabilisation of laser output parameters by monitoring the optical output parameters

Definitions

  • the technical field relates to a laser driving apparatus used in a laser light source for a display use.
  • a laser device including a semiconductor laser unit that emits excited laser light and an optical wavelength conversion element of a nonlinear optical crystal that performs wavelength conversion of the excited laser light, as a fundamental wave, to laser light having a predetermined wavelength has been known.
  • FIG. 1 shows a graph of characteristic showing a relationship between the temperature and optical output of a nonlinear optical crystal when the constant amount of light enters the nonlinear optical crystal from an excitation semiconductor laser unit.
  • FIG. 1 there is an optimum temperature at which the optical output is maximum, and therefore temperature needs to be controlled such that the temperature of the nonlinear optical crystal reaches the optimum temperature.
  • the temperature versus optical output characteristic of the nonlinear optical crystal changes depending on usage environment or a change over time.
  • control is performed such that, when the temperature of the nonlinear optical crystal is shifted from the optimum temperature, the output from the excitation semiconductor laser unit is increased. As a result, a driving current increases.
  • a technique of detecting the increase in driving current and controlling the temperature of the nonlinear optical crystal such that the detected value is a predetermined value is proposed (for example, Japanese Patent Application Laid-Open No. 2001-168439).
  • FIG. 2 is a block diagram showing a configuration of an example of a conventional laser driving apparatus.
  • reference numeral 1 denotes a laser device including semiconductor laser unit 11 as an excitation laser unit that emits excited laser light and nonlinear optical crystal 12 as an optical wavelength conversion element that performs wavelength conversion of the excited laser light, as a fundamental wave, to laser light having a predetermined wavelength.
  • Reference numeral 2 denotes a driving section for causing semiconductor laser unit 11 to emit excited laser light.
  • Reference numeral 3 denotes an optical detection section for detecting an optical output of the laser light whose wavelength is converted, exiting from laser device 1 .
  • Reference numeral 4 denotes an optical output control section for comparing an optical detection value outputted from optical detection section 3 with an optical output target value, to calculate a control value, and outputting the control value to driving section 2 , whereby the optical output of the laser light exiting from laser device 1 reaches the optical output target value.
  • Reference numeral 5 denotes a current detection section for detecting a laser driving current of driving section 2 .
  • Reference numeral 6 denotes an operating temperature setting section for finding a temperature setting value from the current detection value from current detection section 5 .
  • Reference numeral 7 denotes a temperature control section for controlling the temperature of nonlinear optical crystal 12 to match the temperature setting value found by operating temperature setting section 6 .
  • Temperature control section 7 includes a Peltier element (not shown) for heating and cooling nonlinear optical crystal 12 and a temperature detecting element (not shown) that detects a temperature of nonlinear optical crystal 12 .
  • operating temperature setting section 6 provides the temperature T 0 set at the end of a previous operation as an initial temperature setting value to temperature control section 7 , to cause temperature control section 7 to start temperature control.
  • optical output control section 4 operates such that laser device 1 generates a target optical output, and operating temperature setting section 6 stores the current detection value I 0 current detection section 5 detects at this time.
  • operating temperature setting section 6 shifts the temperature setting value to a higher value by a micro-temperature ⁇ T and stores the current detection value I 1 detected at the temperature setting value T 0 + ⁇ T. If I 1 ⁇ I 0 , operating temperature setting section 6 sets the current temperature setting value T 0 + ⁇ T as a new temperature setting value.
  • a laser device composed of a nonlinear optical crystal is useful for, for example, a backlight source of a liquid crystal display.
  • a backlight source of a liquid crystal display it is necessary to adjust light dynamically.
  • PWM pulse width modulating
  • FIG. 3 shows a relationship between the input power and optical output of the laser device and a relationship between the input power and efficiency, for the case of the linear drive method.
  • the optical output from the excitation laser unit is substantially proportional to the input power and the optical output from the nonlinear optical crystal is substantially proportional to a square of the optical output from the excitation laser unit, so that the optical output from the laser device increases in approximately proportional to a square of the input power and the efficiency increases approximately linearly relative to the input power. That is, the efficiency changes relative to the input power.
  • FIGS. 4A to 4C show the relationships between an optical output and efficiency, and the driving current of the laser device in linear drive.
  • the drive voltage of the excitation laser unit is substantially constant, and, consequently, the input power is substantially proportional to the driving current as shown in FIG. 4C .
  • FIG. 4A shows the relationship between the driving current and the optical output. The optical output increases in approximately proportional to a square of the driving current and due to the influence of saturation of the optical output from the excitation laser unit, the optical output from the laser device gets saturated.
  • FIG. 4B shows a relationship between the driving current and the efficiency. The efficiency increases in proportional to the driving current and due to the influence of saturation of the excitation laser unit, the efficiency decreases.
  • FIG. 5 shows the relationship between the average input power and average optical output of the laser device and the relationship between the average input power and efficiency, for the case of a PWM pulse drive method.
  • the amplitude in PWM drive is constant, and so the average value is determined by duty. Consequently, the average optical output increases in proportional to the average input power and the efficiency is constant relative to the average input power. That is, the efficiency does not change relative to the average input power. In this way, in the case of PWM drive, the nonlinear optical crystal always operates at a high efficiency level.
  • PWM drive is more advantageous from an efficient viewpoint, and therefore, the nonlinear optical crystal needs to operate at an optimum temperature further in PWM drive.
  • FIG. 1 showing the relationship between the temperature and optical output of a nonlinear optical crystal when the constant amount of light enters the nonlinear optical crystal from an excitation semiconductor laser unit, there is an optimum temperature at which the optical output is maximum, so that, as in the case of PWM drive, a temperature always needs to be controlled such that the optical output is maximum.
  • the laser driving apparatus achieves the above object by adopting a configuration including: a laser device that includes an excitation laser unit that emits excited laser light and an optical wavelength conversion element that converts the excited laser light, as a fundamental wave, to laser light having a predetermined wavelength, and that emits the laser light, as an optical output, whose wavelength is converted by the optical wavelength conversion element; a driving section that drives the excitation laser unit of the laser device by a pulse current; an optical detecting section that detects an average value of the optical output in a pulse form emitted from the laser device and outputs the average value as an optical detection value; a current detecting section that detects a value corresponding to an average value of the pulse current and outputs the value as a current detection value; an efficiency detecting section that outputs, as an efficiency value, a value obtained by dividing the optical detection value by the current detection value; a maximization control section that receives as input the efficiency value and derives a temperature setting value such that the efficiency value is maximum; and a temperature control section that controls a
  • the present inventors have achieved the present invention by focusing on the fact that, in the case of adjusting light in PWM pulse drive, efficiency is substantially constant when the temperature of a nonlinear optical crystal is constant as shown in FIG. 5 .
  • FIG. 1 is an illustrative graph of dependence on temperature of an optical output of a laser device using a wavelength conversion element
  • FIG. 2 is a block diagram showing a configuration of an example of a conventional laser driving apparatus
  • FIG. 3 is an illustrative graph of input power versus optical output characteristic at linear drive
  • FIG. 4A is an illustrative graph of a drive current versus optical output characteristic (optical output) at linear drive
  • FIG. 4B is an illustrative graph of a drive current versus optical output characteristic (efficiency) at linear drive
  • FIG. 4C is an illustrative graph of a drive current versus optical output characteristic (input power) at linear drive
  • FIG. 5 is an illustrative graph of an average input power versus optical output characteristic at PWM drive
  • FIG. 6A is an illustrative graph of an average driving current versus optical output characteristic (optical output) at PWM drive
  • FIG. 6B is an illustrative graph of an average driving current versus optical output characteristic (efficiency) at PWM drive
  • FIG. 6C is an illustrative graph of an average driving current versus optical output characteristic (average input power) at PWM drive
  • FIG. 7 is a block diagram showing a configuration of a laser driving apparatus according to Embodiment 1 of the present invention.
  • FIG. 8A is an illustrative graph showing an example of the operation of the laser driving apparatus according to Embodiment 1 of the present invention.
  • FIG. 8B is an illustrative graph showing another example of the operation of the laser driving apparatus according to Embodiment 1 of the present invention.
  • FIGS. 6A to 6C show relationships between an average driving current and, an average optical output and efficiency at PWM drive.
  • the drive voltage of a semiconductor laser device is substantially constant, and therefore, the average input power is substantially proportional to the average driving current as shown in FIG. 6C .
  • FIG. 6A shows a relationship between the average driving current and the average optical output.
  • the average optical output increases in proportional to the average driving current.
  • the efficiency is, as shown in FIG. 6B , constant regardless of the average driving current.
  • the above-described efficiency is a ratio of the optical output from a laser device using a nonlinear optical crystal to the input power injected into an excitation semiconductor laser unit.
  • the drive voltage of the semiconductor laser unit is substantially constant, and therefore, the input power is substantially proportional to the driving current of the semiconductor laser unit. Accordingly, the efficiency is the average optical output divided by the average input power, that is, the average optical output divided by the average driving current, and the average optical output per unit average driving current has a value proportional to the efficiency, so that temperature should be controlled so as to maximize this value.
  • FIG. 7 is a block diagram showing a configuration of the laser driving apparatus according to Embodiment 1 of the present invention.
  • reference numeral 1 denotes a laser device including semiconductor laser unit 11 serving as an excitation laser unit that emits excited laser light and nonlinear optical crystal 12 serving as an optical wavelength conversion element that converts the excited laser light having a wavelength, as a fundamental wave, to laser light having a predetermined wavelength.
  • Reference numeral 2 denotes a driving section for driving semiconductor laser unit 11 to cause semiconductor laser unit 11 to emit excited laser light.
  • Reference numeral 3 denotes an optical detection section for outputting an optical detection value, which is a detected average value of an optical output from laser device 1 .
  • Reference numeral 4 denotes an optical output control section for outputting a control value such that the optical detection value from optical detection section 3 matches an optical output target value.
  • Reference numeral 5 denotes a current detection section for outputting a current detection value, which is a detected average value of the laser driving current of driving section 2 .
  • Reference numeral 7 denotes a temperature control section for controlling the temperature of nonlinear optical crystal 12 .
  • Reference numeral 8 denotes a PWM generation section for converting the control value from optical output control section 4 into pulses by PWM, and outputting the pulses to driving section 2 .
  • Reference numeral 9 denotes an efficiency detection section for calculating an average optical output per unit average current, that is, an efficiency value, by dividing the optical detection value detected by optical detection section 3 by the current detection value detected by current detection section 5 .
  • Reference numeral 10 denotes an optical output maximization control section for finding a temperature setting value such that the efficiency value obtained by efficiency detection section 9 is maximum.
  • optical output maximization control section 10 finds a temperature setting value such that this efficiency value is maximum, and temperature control section 7 controls a temperature such that the temperature of nonlinear optical crystal 12 reaches this setting value.
  • PWM generation section 8 converts a control value from optical output control section 4 , which controls an optical output from laser device 1 using nonlinear optical crystal 12 by a deviation between an optical output target value and an optical detection value, into pulses, and causes laser device 1 using nonlinear optical crystal 12 to pulse drive.
  • the efficiency is substantially constant at pulse drive, even when the control value varies and thus the average optical output varies, the efficiency according to the temperature of nonlinear optical crystal 12 at any given time can be kept substantially constant.
  • a value acquired by dividing an average optical output detected by optical detection section 3 by an average driving current detected by current detection section 5 is substantially proportional to the efficiency.
  • efficiency detection section 9 finds this value and optical output maximization control section 10 finds a temperature setting value such that this value is maximum, and then temperature control section 7 controls a temperature of nonlinear optical crystal 12 .
  • temperature control section 7 controls a temperature of nonlinear optical crystal 12 .
  • FIGS. 8A and 8B show the states of the change.
  • FIG. 8A shows an example of a case where a temperature setting value at which an efficiency value is maximum changes to a higher value.
  • FIG. 8B shows an example of a case where a temperature setting value at which an efficiency value is maximum changes to a lower value.
  • FIGS. 8A and 8B are enlarged graphs of a portion in FIG. 1 where the optical output is maximum.
  • a horizontal axis represents the temperature setting value, which is outputted from optical output maximization control section 10 , and which corresponds to the temperature in FIG. 1
  • a vertical axis represents the efficiency value, which is outputted from efficiency detection section 9 , and which corresponds to the optical output in FIG. 1
  • a solid-line represents an initial characteristic
  • a broken-line represents an actual characteristic.
  • the maximum value of the efficiency value of the initial characteristic is Em and the temperature setting value at this time is Tm.
  • Optical output maximization control section 10 stores in advance initial characteristics represented by the solid lines in FIGS. 8A and 8B . Then, when, for example, the laser driving apparatus is turned on, optical output maximization control section 10 outputs the setting temperature T 1 which is lower or higher than the Tm by a predetermined temperature. As a result, optical output maximization control section 10 acquires the efficiency value E 1 as input. Optical output maximization control section 10 finds the temperature setting value T 2 obtained by applying E 1 to the initial characteristic, regards a difference between T 1 and T 2 as Td, which is the amount of change over time of Tm, and outputs the temperature setting value T obtained by adding Td to Tm, to temperature control section 7 as a temperature setting value at which the efficiency value is maximum.
  • temperature control section 7 controls the temperature of nonlinear optical crystal 12 . This makes it possible to control a temperature such that the optical output is maximum, even when adjusting light where an arbitrary optical output target value is provided.
  • optical output maximization control section 10 accepts as input a current detection value from current detection section 5 . Then, in a range where the current detection value is smaller than a predetermined value, optical output maximization control section 10 does not perform a control operation and holds a previous value.
  • control is more stable when the current detection value increases. For this reason, the control may be performed when the current detection value is close to a maximum value.
  • current detection section 5 detects an average driving current of driving section 2 .
  • a control value outputted from optical output control section 4 may be detected, a duty cycle of an output from PWM generation section 8 or driving section 2 may be detected, or a duty cycle of an optical output from laser device 1 may be detected.
  • efficiency detection section 9 finds an efficiency value by dividing an optical detection value by a current detection value.
  • a value obtained by sampling a pulse amplitude value of an optical output from laser device 1 may be used as an efficiency value.
  • Embodiment 2 of the present invention is the same as in Embodiment 1 shown in FIG. 7 but the operation of optical output maximization control section 10 is different.
  • the operation of optical output maximization control section 10 in the present embodiment is similar to operating temperature setting section 6 shown in FIG. 2 . The operation will be described below.
  • Optical output maximization control section 10 first receives as input the efficiency value E 0 for the current temperature setting value T 0 . Then, optical output maximization control section 10 outputs the temperature setting value T 0 + ⁇ T obtained by changing T 0 to a higher value by the micro value ⁇ T, and receives the efficiency value E 1 as input. If E 1 is greater than E 0 , optical output maximization control section 10 holds T 0 + ⁇ T as the temperature setting value. If E 1 is smaller than E 0 , optical output maximization control section 10 outputs the temperature setting value T 0 ⁇ T obtained by changing T 0 to the low-temperature side by the micro value ⁇ T, and receives the efficiency value E 2 as input.
  • optical output maximization control section 10 If E 2 is greater than E 0 , optical output maximization control section 10 holds T 0 ⁇ T as the temperature setting value. If E 2 is smaller than E 0 , optical output maximization control section 10 resets the temperature setting value to T 0 and holds T 0 . By the above-described operation, optical output maximization control section 10 outputs a temperature setting value at which the efficiency value is maximum, to temperature control section 7 .
  • temperature control section 7 controls a temperature of nonlinear optical crystal 12 , by the temperature setting value found by optical output maximization control section 10 .

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  • Physics & Mathematics (AREA)
  • Condensed Matter Physics & Semiconductors (AREA)
  • General Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Optics & Photonics (AREA)
  • Optical Modulation, Optical Deflection, Nonlinear Optics, Optical Demodulation, Optical Logic Elements (AREA)
  • Semiconductor Lasers (AREA)
  • Lasers (AREA)
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JP2008132764A JP5098803B2 (ja) 2008-05-21 2008-05-21 レーザ駆動装置

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CN112582871B (zh) * 2020-12-14 2022-02-22 中国科学院合肥物质科学研究院 一种脉冲激光序列能量校正系统及方法
NL2028674B1 (en) * 2021-07-09 2023-01-16 Nearfield Instr B V Laser diode arrangement, method of operating a laser diode and scanning microscope device comprising a laser diode

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US5168503A (en) * 1990-11-15 1992-12-01 Pioneer Electronic Corporation Harmonic generator
US5265115A (en) * 1991-08-30 1993-11-23 Hoya Corporation Solid-state laser device having a feedback loop
US5341388A (en) * 1992-02-20 1994-08-23 Sony Corporation Laser light beam generating apparatus
JP2001168439A (ja) 1999-12-09 2001-06-22 Fuji Photo Film Co Ltd 発光装置
JP2003174222A (ja) 2001-12-06 2003-06-20 Shimadzu Corp レーザ装置
JP2003298180A (ja) 2002-03-29 2003-10-17 Fuji Photo Film Co Ltd 半導体レーザ駆動装置
US20080175286A1 (en) * 2007-01-23 2008-07-24 Seiko Epson Corporation Light source device, control method therefor, lighting device, monitor device, and image display device

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JPH1020351A (ja) * 1996-07-01 1998-01-23 Sony Corp レーザ光源装置および当該装置の制御方法
JP2001267680A (ja) * 2000-03-22 2001-09-28 Matsushita Electric Ind Co Ltd レーザ光発生装置および光学的記録特性評価装置
JP4914083B2 (ja) * 2005-06-30 2012-04-11 キヤノン株式会社 光波長変換装置、光波長変換方法、及びそれを用いた画像形成装置
JP2007233039A (ja) * 2006-03-01 2007-09-13 Ntt Electornics Corp 波長変換装置、コンピュータプログラム及びコンピュータ読み取り記録媒体

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5168503A (en) * 1990-11-15 1992-12-01 Pioneer Electronic Corporation Harmonic generator
US5265115A (en) * 1991-08-30 1993-11-23 Hoya Corporation Solid-state laser device having a feedback loop
US5341388A (en) * 1992-02-20 1994-08-23 Sony Corporation Laser light beam generating apparatus
JP2001168439A (ja) 1999-12-09 2001-06-22 Fuji Photo Film Co Ltd 発光装置
JP2003174222A (ja) 2001-12-06 2003-06-20 Shimadzu Corp レーザ装置
JP2003298180A (ja) 2002-03-29 2003-10-17 Fuji Photo Film Co Ltd 半導体レーザ駆動装置
US20080175286A1 (en) * 2007-01-23 2008-07-24 Seiko Epson Corporation Light source device, control method therefor, lighting device, monitor device, and image display device

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US20090290609A1 (en) 2009-11-26
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